The present invention relates to a new and improved coupling assembly which is utilized to transmit force to either rotate a member or hold the member against rotation.
A known coupling assembly is utilized to either rotate a machine input shaft or to hold the machine input shaft against rotation. This coupling assembly includes a flywheel which is connected with a machine input shaft by a clutch assembly to rotate the machine input shaft when a brake assembly is in a disengaged condition. When the clutch assembly is in a disengaged condition, the brake assembly holds the machine input shaft against rotation.
The brake assembly utilized in this known coupling assembly is of the drum type and includes a pair of pivotally interconnected brake shoes which are pressed against a brake drum by springs. A fluid piston/cylinder chamber is operable to actuate the brake assembly to a disengaged condition.
The brake and clutch assemblies in this known coupling assembly are sequentially operated upon actuation of a control valve to simultaneously direct fluid pressure to both the brake assembly and the clutch assembly. Thus, upon actuation of the control valve, the clutch assembly is operated from the disengaged condition to the engaged condition at a low pressure, for example, 10 psi. The brake assembly is subsequently operated from the engaged condition to the disengaged condition at a higher pressure, for example, 65 psi.
Although generally satisfactory in its mode of operation, this known coupling assembly may be considered to be inadequate for certain uses due to an inability of the brake assembly to consistently provide adequate braking effort. This is particularly true when the coupling assembly is used in an environment in which the brake assembly is exposed to contaminants. Thus, machine lubricating oil is a contaminant when it enters the brake assembly. The lubricating oil decreases the force which the brake assembly can exert to stop a rotating input shaft or member. Although it is desirable to keep lubricating oil out of the brake assembly, cooling air should circulate through the brake assembly in order to prevent brake fade during extensive use. In addition, it is desirable to maintain the spring force which actuates the brake assembly as constant as possible with wear of the brake shoes.